Hepatic gluconeogenesis is necessary during starvation, stress and is accelerated in diabetes mellitus; it is regulated by changes in substrate and cofactor concentrations and enzyme activities in turn regulated by hormones. Regulation of this process has been studied mainly in rats. Studies with other species suggest that rats may be a somewhat improper model for gluconeogenesis in humans due to such things as a difference in cellular location of phosphoenolpyruvate carboxy-kinase (PEPCK) and the redox state of their mitochondria. Fatty acids enhance gluconeogenesis in rats but exert no effect on or inhibit this process in other species. We find fasted rabbits to have a distribution of hepatic PEPCK similar to humans. Lactate-, dihydroxyacetone- and fructose-derived gluconeogenesis in rabbits is enhanced by glucagon, epinephrine and cyclic AMP and regulation of gluconeogenesis appears somewhat different in rabbits vs. rats. These effectors appear to influence the interconversions of fructose 1.6-bisphosphate and fructose 6-phosphate and of P-enolpyruvate and pyruvate. We will use perfused livers and hepatocytes to investigate questions such as: is the effect of epinephrine mediated via alpha- or beta-adrenergic sites; are the gluconeogenic influences of these effectors on fructose 1.6-bisphosphatase, phosphofructokinase and/or pyruvate kinase and what are their influences on glycogenolysis as mediated by phosphorylase? The influence of somatostatin and Ca2 ion alone with various effectors will be examined for their own influences and for their potential as tools to study mechanisms of action of other effectors. L-tryptophan and quinolinate inhibit hepatic gluconeogenesis and increase the assayable activity of PEPCK in normal rats and their perfused livers respectively; yet these two compounds are ineffective in diabetic rats. Structural and kinetic properties of PEPCK from normal, diabetic and tryptophan-treated rats will be investigated to explain this curious observation and also to define characteristics of a key enzyme of gluconeogenesis which heretofore has received little attention. We suggest that tryptophan may normally regulate gluconeogenesis and that such regulation is altered in diabetes. We will investigate exogeneous quinolinate's ability to enter diabetic perfused livers and isolated hepatocytes.